Method of making package for photographic film

ABSTRACT

A thinner, less-expensive-to-produce, and more easily handled, opaque sheet is formed by coextrusion of two polymeric layers containing relatively low loadings of black pigment around a third layer of polymer which is pigmented at levels higher than would be practical using conventional extrusion processes, rather than a coextrusion procedure. The sheet is an improved product for use in packaging photographic film or like products to be protected from light.

This is a division of application Ser. No. 774,934 filed Mar. 7, 1977,now U.S. Pat. No. 4,174,038.

BACKGROUND OF THE INVENTION

It has long been the practice to package light-sensitive photographicfilm in opaque packages, usually black packages formed of layers ofblack-pigmented paper and/or plastic layers. One package, typical of thebest being used, is formed of a packaging sheet constructed of thefollowing layers:

(1) black paper--obtained from paper manufacturers

(2) a coating of about 0.001 inch of polyethylene containing 10% ofcarbon black pigment

(3) another coating like coating (2) coated over coating (2).

The sheet described above comprises 2 mils of polyethylene, in additionto the thickness of the black paper, and is wholly acceptable in meetingthe required degree of opacity for film packaging which can be generallydescribed as that degree of opacity which will protect a 1000 ASA-speedfilm from a 5000 watt lamp placed close to the package. Nevertheless,this pigmented polyethylene sheet of the art is relatively expensive andless flexible than is desirable. Applicant set out to provide animproved package, one that is more easily handled and which requiresless carbon black filler.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a process whereby animproved, more easily manipulated, and less expensive opaque packagingpaper may be produced.

Another object of the invention is to provide an improved opaque sheet,one which is more flexible, more dependably opaque, and less expensiveto make.

Still another object of the invention is to provide a novel opaquepackage.

Another object of the invention will be obvious to those skilled in theart on reading the present disclosure.

The above objects have been substantially achieved by utilizing aprocess whereby a very high loading of carbon black in acentrally-located polymeric matrix is carried through the die of anextruder while sandwiched between two outer layers of polymer. The outerlayers have from 0 to 8% carbon black therein and protect the centrallayer from contact with the hot extrusion die. Consequently, severerheological and sticking problems associated with contact of such dieswith a highly-loaded polymer, e.g. one containing 20 to 25% by weight ofcarbon black are wholly avoided. A smooth extrudate is achieved withminimal build up of material on the die surfaces. The practicalconsequence of this procedure allows the loading of the polymer layer sothat it comprises an advantageously-high loading of carbon black,thereby reducing the total amount of carbon black that must be used inthe system. The amount of polymer that must be used is also reduced andallows a marked reduction in the gauge of the overall packaging sheetwhich must be used to achieve the desired opacity. In sum, thesemodifications allow a suitably opaque product to be produced which isless expensive and more flexible while simultaneously providing abetter-protected and improved opaque barrier within the product.

The outer layers of polymer are advantageously polyethylene containing 0to 10% carbon black. Loadings of 5 to 8% are preferred as a balancebetween optimum extrudability and an achieving a supplemental opacitycharacteristic for the central opaque barrier layer. These outer layersare about 0.0005 inches thick. The central layer contains 15 to 25%carbon black and is also about 0.0005 inches thick. It should beunderstood that the term "layer" is used to facilitate description ofthe invention. The coextruded polymer is really a single layer bestconstrued as three distinguishable zones of polymer melt-bonded to forma single extruded web. The coextruded ply is up to about 2 mils inthickness.

In the prior art, the black paper used in manufacture of opaquepackaging materials has usually been a paper of a weight of 70-80 lbsper ream. In the present invention, with the protective value of a thickouter paper minimized by the concentration of carbon black in aninterior coating, it is possible to drop the paper to a thinnermaterial, e.g. to a paper in the 15 lbs-to 40 lbs range. Indeed, it ispossible to dispense entirely with carbon black in the paper layer. Itis also possible to use the product of the invention to replace evenfoil-bearing laminates of the prior art in those applications whereinvisible light is the radiation to be absorbed by the packaging material.

Although the invention is described with respect to polyethylene, andthe advantages over the prior art processes and products areparticularly emphatic with respect to products utilizing low density andmedium density polyethylene polymer, it is to be further emphasized thatthe process of the invention will allow substitution of a differentpolymer composition, i.e. a more abrasion resistant polymer in eitherone or both of the lower-pigmented exterior zones of the sheet of theinvention. Moreover, metallic and other selected inorganic fillers canbe included in the interior zones of polymer and, when used, they can beselected to achieve an even wider range of opacity, e.g. aluminum can beused to absorb infra-red radiation.

The carbon black pigment is suitably an oil furnace carbon block havinga nominal sub-micron particle size and surface area of from 25-150square meters per gram.

ILLUSTRATIVE EXAMPLES OF THE INVENTION

In this application and accompanying drawings, there is shown anddescribed a preferred embodiment of the invention and suggested variousalternatives and modifications thereof, but it is to be understood thatthese are not intended to be exhaustive and that other changes andmodifications can be made within the scope of the invention. Thesesuggestions herein are selected and included for purposes ofillustration in order that others skilled in the art will more fullyunderstand the invention and the principles thereof and will be able tomodify it and embody it in a variety of forms, each as may be bestsuited in the condition of a particular case.

IN THE DRAWINGS

FIG. 1 is a section of an opaque package formed according to theinvention.

FIGS. 2 through 4 are schematic sectional views of packaging materialsconstructed according to the invention.

Referring to FIG. 2, it is seen that a packaging sheet material 10 isformed a polymeric web 12 which has been coextruded and laminated to awhite paper 14 weighing about 17 lbs per ream and formed of a pulpcommonly known to those skilled in the paper art as Bleached MO pulp.Web 12 comprises two outer zones 16 comprising medium densitypolyethylene loaded with about 7% carbon black. Inner zone 17 comprisesa loading of 20% carbon black. Each zone is ideally about 0.0005 inchesthick and, in any event, web 12 is about 0.0015 inches thick.

The coextrusion and lamination are carried out using manipulativeprocedures well known in the art.

FIG. 4 illustrates a sheet material 30, comprising a carbon blackpigmented paper 34, and a coextruded layer 32 which is laminated to thepaper and comprises polyethylene zone 36 containing 5% carbon black anda zone 37 comprising 19% carbon black.

FIG. 1 illustrates a package for photographic film formed of thepackaging material, production of which is described in FIG. 2. Thepackage is readily tearable because of the relative thinness of thepackaging material and, also, because of the relative brittleness of theheavily-loaded central layer of the extruded melt. Thus, film roll 50 issecurely packaged within the heat sealed material formed of thepackaging sheet of FIG. 3.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which mightbe said to fall therebetween.

What is claimed is:
 1. A process of forming an opaque barrier layer ofpolyethylene and carbon black comprising the coextrusion of a centrallayer of polyethylene containing from 15 to 25% carbon black, betweentwo exterior layer of polyethylene which comprises from 0 to 10 percentcarbon black and wherein such extrusion is through a hot extrusion dieand said exterior layers are zones forming means to minimize build-up ofthe material being extruded on the surfaces of said die and to protectsaid central layer from contact with said die and thereby achieve asmooth extrudate of high carbon content.
 2. A process defined in claim 1wherein said carbon black is an oil furnace carbon black of nominalsub-micron size.